The Universal Mobile Telecommunication System (UMTS) is one of the third generation mobile communication technologies designed to succeed GSM. 3GPP Long Term Evolution (LTE) is a project within the 3rd Generation Partnership Project (3GPP) to improve the UMTS standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. The Universal Terrestrial Radio Access Network (UTRAN) is the radio access network of a UMTS and Evolved UTRAN (E-UTRAN) is the radio access network of an LTE system. In an UTRAN and an E-UTRAN, a user equipment (UE) is wirelessly connected to a Base Station (BS) commonly referred to as a NodeB and an evolved NodeB (eNodeB) respectively. Each BS serves one or more areas referred to as cells.
The possibility of identifying the geographical location of users in the wireless networks has enabled a large variety of commercial and non-commercial services, e.g., navigation assistance, social networking, location-aware advertising, and emergency services. Different services may have different positioning accuracy requirements imposed by the application. Furthermore, some regulatory requirements on the positioning accuracy for basic emergency services exist in some countries, such as E911 from the Federal Communications Commission (FCC) in US and corresponding E112 in Europe.
In many environments, the position may be accurately estimated by using positioning methods based on Global Positioning System (GPS). However, GPS is known to be associated with high costs due to higher UE complexity, a relatively long time to first positioning fix, and a high UE energy consumption due to a need for large computational resources, resulting in fast battery drain. Today's networks often have a possibility to assist UEs in order to improve the terminal receiver sensitivity and the GPS startup performance through Assisted-GPS (A-GPS) positioning. However, GPS or A-GPS receivers are not necessarily available in all wireless UEs, and some wireless communications systems do not support A-GPS. Furthermore, GPS-based positioning may often have unsatisfactory performance in urban canyons and indoor environments. There is therefore a need for complementary terrestrial positioning methods. There are a number of different terrestrial positioning methods. One example is Observed Time Difference of Arrival (OTDOA) in LTE.
Nevertheless, methods with traditionally lower accuracy such as those exploiting cell identities or fingerprints are still of high importance and may become particularly important for dense wireless network deployments. In dense network deployments the coverage area of lower power BSs is typically small and the resulting positioning results may therefore be quite accurate. These positioning results are also achievable at a very short response time, and with low complexity and resource consumption. Low resource consumption is particularly important for talk time and standby device performance.
The three key network elements in an LTE positioning architecture are the Location Services (LCS) Client, the LCS target and the LCS Server. The LCS Server is a physical or logical entity managing positioning for an LCS target by collecting measurements and other location information, assisting the UE in performing measurements when necessary, and estimating the LCS target location. An LCS Client is a software and/or hardware entity that interacts with an LCS Server for the purpose of obtaining location information for one or more LCS targets. The LCS target is the entity that is being positioned. LCS Clients may reside in the LCS targets themselves. In the positioning procedure, an LCS Client sends a positioning request to an LCS Server to obtain location information, and the LCS Server processes and serves the received request and sends the positioning result and optionally a velocity estimate to the LCS Client. The positioning request may originate from the UE or the network.
In LTE, there exist two positioning protocols operating via the radio network: the LTE Positioning Protocol (LPP) and the LTE Positioning Protocol annex (LPPa). The LPP is a point-to-point protocol between the LCS server and the LCS target, used for the positioning of the LCS target. LPP may be used both in a user plane and a control plane positioning procedure, and multiple LPP procedures are allowed in series and/or in parallel thereby reducing latency. LPPa is a protocol between the eNodeB and the LCS server specified only for control plane positioning procedures, although it still may assist user plane positioning by the querying of eNodeBs for information and measurements. A Secure User Plane Location (SUPL) protocol is used as a transport protocol for LPP in the user plane.
A block diagram illustrating an example of a high-level positioning architecture is given in FIG. 1. The LCS target is a UE 150, and the LCS server 100 is an Evolved Serving Mobile Location Center (E-SMLC) 101. The LCS server 100 may also comprise a SUPL Location Platform (SLP) 102. The control plane positioning protocols LPP between the UE 150 and the E-SMLC 101, LPPa between an eNodeB 130 and the E-SMLC 101, and LCS-Application Protocol (AP) between a Mobile Management Entity (MME) 120 in a Core Network (CN) and the E-SMLC 101, are illustrated with arrows. The user plane positioning protocols are also illustrated and comprises SUPL/LPP between the UE 150 and the SLP 102, and the SUPL between the UE 150 and the SLP 102. The SLP 102 may comprise two components, a SUPL Positioning Center (SPC) and a SUPL Location Center (SLC), which may also reside in different nodes. In an example implementation, the SPC has a proprietary interface with the E-SMLC 101, and Llp interface with the SLC, and the SLC part of the SLP communicates with a Packet data network GateWay (P-GW) 160 and an external LCS Client 110. Additional positioning architecture elements may also be deployed to further enhance performance of specific positioning methods. For example, deploying radio beacons 140 is a cost-efficient solution which may significantly improve positioning performance indoors and also outdoors by allowing more accurate positioning, for example, with proximity location techniques.
Positioning Results May be Signaled Between:
                The LCS target 150 and the LCS server 100, e.g. over the LPP;        LCS/positioning servers 100, such as between the E-SMLC and the SLP, over standardized or proprietary interfaces;        The LCS/positioning server 100 and other network nodes, such as between the E-SMLC and the MME, a Mobile Switching Centre (MSC), aGateway Mobile Location Center (GMLC), Operation and Maintenance (O&M) nodes or Self Organizing Nodes (SON);        The LCS/positioning server 100 and the LCS client 110, such as between the E-SMLC and a Public Safety Answer Point (PSAP) or between the SLP and an external LCS client.        
To meet Location Based Services (LBS) demands, the LTE network will deploy a range of complementing methods characterized by different performance in different environments. Depending on where the measurements are conducted and the final position is calculated, the methods may be UE-based, UE-assisted or network-based, each with its own advantages. The following methods are available in the LTE standard for both the control plane and the user plane:                Cell Identity (CID) positioning;        UE-assisted and network-based Enhanced-CID (E-CID), including network-based Angle of Arrival (AoA) positioning;        UE-based and UE-assisted A-GPS positioning, or the more general Assisted Global Navigation Satellite System (A-GNSS) positioning; and        UE-assisted OTDOA positioning.        
Hybrid positioning methods, fingerprinting positioning, and Adaptive ECID (AECID) do not require additional standardization and are therefore also possible in LTE. Furthermore, there may also be UE-based versions of the methods above, e.g. UE-based GNSS/GPS, and UE-based OTDOA. There may also be some alternative positioning methods such as civic address based positioning or proximity based location. Uplink Time Difference Of Arrival (UTDOA) currently under discussion in 3GPP may also become standardized in a coming LTE release.
CID Positioning:
Cellular systems are divided into cells, each cell served by one specific BS. Each BS may serve more than one cell. One important point from a positioning and navigation perspective is that the cell where a specific UE is located is known in the cellular system. Hence, after determination of the geographical area covered by a specific cell, it may be stated that the UE is located somewhere within said geographical area, as long as it is connected and the reported cell identity of the serving cell is equal to the cell identity of the particular geographical area. In several systems, the preferred representation of the geographical area of the cell is given by the cell polygon format. The cell area described by a polygon is an approximation, and the polygon is normally pre-determined in the cell-planning tool to represent the cell area with a certain confidence. The confidence is the probability that the terminal is actually located within the reported area, in this case bounded by the cell polygon. Although the accuracy of the method is limited by the cell range, its main advantages are a very low response time as well as the fact that it has no impact on the UE, it is easy to implement, and it is widely spread and always available where there is cellular coverage. To exploit these advantages and enhance the CID technique, the accuracy of CID is further improved in the E-CID method.
E-CID Positioning:
E-CID methods exploit four sources of position information: the CID and a corresponding geographical description of the serving cell, a Timing Advance (TA) of the serving cell, the CIDs and corresponding signal measurements of measured cells, which may be up to 32 cells in LTE, including the serving cell, as well as AoA measurements. The following techniques are commonly used for E-CID:                CID and TA: A combination of the geographical cell description, the eNodeB position, and the distance between the eNodeB and the UE obtained from a TA measurement;        Signal strength: Distance measures are derived from signal strengths measured in the UE and combined with cell polygons as for CID and TA;        AoA: As an example the angle of a UE with respect to a reference direction which is the geographical North may be defined.        AoA combined with TA, exploiting the orthogonal directionality of the two involved measurements.        
TDOA or Time of Arrival (TOA) Based Methods Such as OTDOA, UTDOA or GNSS/A-GNSS:
OTDOA is a method based on time difference measurements conducted on downlink positioning reference signals received from multiple locations, where the user location is further calculated by multi-lateration. UTDOA, which is an uplink version of OTDOA, is a method that exploits uplink time of arrival or time difference of arrival measurements performed at multiple receiving points. The UTDOA measurements are to be based on Sounding Reference Signals (SRS). A-GNSS/GNSS is a group of methods using satellite signal measurements, where GPS developed in the US and Galileo developed in Europe are some examples of GNSS systems with close to global coverage.
Radio Frequency (RF) Fingerprinting:
The method exploits received signal strength measurements from the UE together with the corresponding cell identities to map onto a predetermined geographical map of the radio properties. The maps may be obtained by extensive site surveying or by radio signal strength simulation software.
AECID:
The AECID method enhances fingerprinting positioning performance by extending the number of radio properties that are used. At least CIDs, TA and AoA may be used in addition to received signal strengths. Corresponding databases are automatically built up by collecting high precision OTDOA and A-GNSS positions, tagged with measured radio properties. The AECID procedure comprises the following steps for building up information supporting the positioning:                1. Tagging of high-precision position results (e.g. A-GPS measurements) with at least one of CIDs of detected cells, auxiliary connection information (e.g. radio access bearer and time), and quantized auxiliary measurements (e.g. TA or signal strength).        2. Collection of all high precision measurements with the same tag in high precision measurement clusters.        3. Calculation of a tagged polygon which contains a pre-specified fraction of said clustered high precision position measurements in the interior, thereby providing a polygon with a known confidence value. The confidence is the probability that the UE is actually located in the reported area.        4. Storage of said tagged polygons in a database of polygons.        
When an AECID positioning is to be performed, the following steps are performed:                a) Determination of at least one of CIDs of detected cells, auxiliary connection information, and quantized auxiliary measurements;        b) Formation of the tag;        c) Retrieval of the polygon corresponding to said tag, from the information built up as described above.        d) Reporting of said polygon.        
According to the 3GPP definition, a heterogeneous network comprises two or more layers, where each layer is served by one type of BS class or type. A heterogeneous network may enhance capacity in dense traffic areas or hotspots and may also be used for coverage extension. One example is a two-layered macro/femto heterogeneous network, where the macro cell layers and femto cell layers typically comprise macro BS and home BS, respectively. A home BS, sometimes also called a femto BS, typically serves private premises or small office environment. Another main characteristic of the home BS is that it is typically owned by a private subscriber. An access control mechanism for the home BS decides if a given UE may or may not connect to that home BS. In UTRAN and E-UTRAN, a concept of Closed Subscriber Groups (CSG) exists. According to the CSG concept only a subset of UEs, defined by the owner of the home BS, may wirelessly access or connect to that particular home BS. Hence wireless access for other UEs is denied by the CSG based home BS. Therefore different cell reselection rules will apply for different UEs with CSG cells in the macro deployment area. This is not taken into account in conventional positioning methods that are based on cell identities, which may make the positioning results inaccurate.